A mother and her child visit a bronze statue of a gorilla outside the Cincinnati Zoo’s Gorilla World exhibit, two days after a boy tumbled into its moat.
Photograph: William Philpott/Reuters

The director of the Cincinnati zoo, where a large gorilla was shot dead on Saturday after a three-year-old boy entered its enclosure, said staff made the right decision in killing the prize ape.

Speaking at a briefing on Monday afternoon, Thane Maynard said messages of support had come in from up to 1,000 animal experts and fans around the world, including the famed British primate expert Jane Goodall.

“She sent her sympathy,” Maynard said.

The gorilla, a 17-year-old, 400lb adult male silverback lowland gorilla named Harambe, was shot after he began dragging the boy by his ankle around a moat within the enclosure at the zoo. Maynard said the child was in imminent danger because the gorilla was agitated and acting erratically.

“This child was being dragged around and his head was banging on the concrete,” Maynard said, responding to suggestions that the gorilla may have just been trying to protect the child and should not have been shot. “This was not a gentle thing.

Maynard said criticism of the zoo on social media was “Monday morning quarterbacking” and said anyone who disagreed did not understand primates and was “not there”, having to deal with the emergency.

The child, who has not been named, was inside the enclosure for 10 minutes before trained staff killed the gorilla with a single rifle shot.

“The risk was down to the power of the animal, his strength,” said Maynard, adding that Harambe could crush a coconut with one hand. Staff at the zoo have been in tears, he said, despite the messages of support.

Maynard insisted the zoo and the barriers at its gorilla enclosure were safe, but then said it was all under review and he did not know if there would be changes to the enclosure when the Gorilla World habitat reopened, perhaps by Saturday. He also said he did not want to point fingers and would not criticize the family of the boy.

He added: “Everybody should keep a hold of their kids, keep an eye on them, here or anywhere, the shopping mall, going to school. But the zoo is a safe place.”

Maynard said the boy had apparently climbed over a 3ft steel fence, which has been in place for 38 years without being scaled, then pushed his way through bushes to the edge of the sunken ape habitat.

The boy then fell 15ft into the shallow moat. The exclamations of onlookers drew Harambe’s attention. Onlookers took video of the boy being dragged swiftly across the moat. Maynard added that, out of sight, the gorilla had also carried the boy up a ladder.

Earlier, animal lovers and activists formed a Memorial Day vigil near the gorilla enclosure, which was closed to the public. Flowers and notes had been left in tribute.

The family of the boy was said to be thankful he survived and aware of criticism sweeping across social media. The mother was identified on Monday morning as Michelle Gregg of Cincinnati, as a Facebook post written by her was quoted online. The post was deleted but a family spokeswoman, Gail Myers, confirmed to the Guardian it was genuine, and said Gregg did not want to release any more information.

In part, the deleted Facebook post said: “God protected my child until the authorities were able to get to him. My son is safe and was able to walk away with a concussion and a few scrapes … no broken bones or internal injuries …

“As a society we are quick to judge how a parent could take their eyes off of their child and if anyone knows me I keep a tight watch on my kids. Accidents happen.”

One of those attending the vigil on Monday said he was not there to point fingers. Anthony Seta of Cincinnati told the Associated Press the death of the gorilla was “a senseless tragedy”.

The gorilla, a member of an endangered species, was born in captivity in the US.

“People can shout at the parents and people can shout at the zoo,” said Seta. “The fact is that a gorilla that just celebrated his birthday has been killed.”

“I was just trying to make a tribute and it’s really taken off from there,” Kate Villanueva of Erlanger, Kentucky, told the AP of the page she created. “I do think there’s a degree of responsibility they have to be held to. You have to be watching your children at all times.”

People for the Ethical Treatment of Animals (Peta) released a statement from its primatologist, Julia Gallucci, saying the zoo should have had better barriers between humans and gorillas.

“This tragedy is exactly why Peta urges families to stay away from any facility that displays animals as sideshows for humans to gawk at,” the statement said.

The three-year-old boy was taken to Cincinnati hospital medical center, and released on Saturday night. In a statement on Sunday, the boy’s family acknowledged the dilemma faced by zoo staff.

“We extend our heartfelt thanks for the quick action by the Cincinnati Zoo staff,” the statement read. “We know that this was a very difficult decision for them, and that they are grieving the loss of their gorilla.”

The family has issued no formal statements since then. On Monday, Myers told the Guardian: “They are doing OK … they are just really thankful … thankful that he is safe.”

Jerry Stones, a zookeeper who raised Harambe at the Gladys Porter zoo in Brownsville, Texas, reportedly spent Sunday in tears. But he refused to condemn staff for shooting the gorilla.

According to a report in the New York Daily News, Stones said the animals are usually “gentle giants”.

At the Cincinnati zoo, Thane Maynard said Harambe had not been mature enough to breed but the zoo had frozen sperm from him, so his “gene pool” would continue.